Hydraulic power transmission assemblies and fluid distribution systems may utilize a vane-type pump. Such pumps typically have a rotor with a plurality of circumferentially spaced vanes rotatably carried by the rotor and slidable relative thereto in slots provided in the rotor. The rotor and vanes cooperate with the internal contour of a containment ring or eccentric ring eccentrically mounted relative to an axis of the rotor and vanes to create fluid chambers between the containment ring or eccentric ring, rotor and vanes. Due to the eccentricity between the containment ring or eccentric ring and the rotor and vanes, the fluid chambers change in volume as they are moved with the rotating rotor and become larger in volume as they are moved across an inlet port and smaller in volume across an outlet port. To vary the eccentricity between the containment ring or eccentric ring and the rotor, the containment ring or eccentric ring may be pivoted upon a fixed axis in a pump housing. Pivoting the containment ring or eccentric ring varies the change in volume of the fluid chambers in use of the pump and hence, varies the displacement characteristic of the pump.
Side plates carried by the pump housing enclose the containment ring or eccentric ring, the rotor and the vanes, and provide passages through which fluid flows to and from the rotor and vanes. These passages, along with timing grooves and the containment ring or eccentric ring contour define pump cycles or zones, namely a fill or inlet zone, a precompression zone from the inlet to the outlet, a displacement or discharge zone, and a decompression zone from the outlet to the inlet.
In current vane-type pumps, the containment ring or eccentric ring is pivoted and oriented by a fluid pressure signal applied to a piston or directly to the containment ring which pivots the containment ring or eccentric ring against the bias of a fixed spring. In other words, a single fluid pressure signal is used to pivot the containment ring or eccentric ring. Accordingly, the control of the containment ring or eccentric ring is essentially limited to a pressure relief type control wherein the containment ring or eccentric ring is pivoted against the bias of the spring only when a sufficient pressure is applied to the piston or containment ring or eccentric ring. When the fluid pressure applied to the piston is not sufficient to move the containment ring or eccentric ring against the bias of a fixed spring, the position of the containment ring or eccentric ring is determined by the spring which limits to one regulation profile characteristic.
Additionally, it has been recognized that for efficient and quiet operation of a vane-type pump it is desirable to maintain the vanes in continuous contact with the containment ring or eccentric ring. Some vane-type pumps depend upon centrifugal force to maintain the contact between the vanes and the containment ring or eccentric ring. These pumps may lack positive and continuous contact between the vane and containment ring or eccentric ring resulting in adverse wear and decreased pump performance. One method to improve the contact between the vanes and the containment ring or eccentric ring involves applying a discharge fluid pressure to chambers or slots in the rotor in which the vanes are received. The fluid pressure drives the vanes radially outwardly and into contact with the containment ring or eccentric ring. However, in at least some conditions, the vanes have a tendency to remain in the rotor slots and the centrifugal force of the spinning rotor is not sufficient to overcome the viscous drag force on the vanes. Without the vanes extending radially outwardly from the rotor, the rotating rotor displaces little if any fluid such that there is little or no discharge pressure. Accordingly, there is little or no discharge pressure communicated to the vane slots and tending to force the vanes radially outwardly from the rotor. Hence, the pump will not prime.